The immune system of a mammal is one of the most versatile biological systems as probably greater than 1.0×107 antibody specificities can be produced. Indeed, much of contemporary biological and medical research is directed toward tapping this repertoire. During the last decade there has been a dramatic increase in the ability to harness the output of the vast immunological repertoire. The development of the hybridoma methodology by Kohler and Milstein has made it possible to produce monoclonal antibodies, i.e., a composition of antibody molecules of a single specificity, from the repertoire of antibodies induced during an immune response.
Unfortunately, current methods for generating monoclonal antibodies are not capable of efficiently surveying the entire antibody response induced by a particular immunogen. In an individual animal there are at least 5–10,000 different B-cell clones capable of generating unique antibodies to a small relatively rigid immunogens, such as, for example dinitrophenol. Further, because of the process of somatic mutation during the generation of antibody diversity, essentially an unlimited number of unique antibody molecules may be generated. In contrast to this vast potential for different antibodies, current hybridoma methodologies typically yield only a few hundred different monoclonal antibodies per fusion.
Other difficulties in producing monoclonal antibodies with the hybridoma methodology include genetic instability and low production capacity of hybridoma cultures. One means by which the art has attempted to overcome these latter two problems has been to clone the immunoglobulin-producing genes from a particular hybridoma of interest into a procaryotic expression system. See, for example, Robinson et al., PCT Publication No. WO 89/0099; Winter et al., European Patent Publication No. 0239400; Reading, U.S. Pat. No. 4,714,681; and Cabilly et al., European Patent Publication No. 0125023.
The immunologic repertoire of vertebrates has recently been found to contain genes coding for immunoglobulins having catalytic activity. Tramontano et al., Sci., 234:1566–1570 (1986); Pollack et al., Sci., 234:1570–1573 (1986); Janda et al., Sci., 241:1188–1191 (1988); and Janda et al., Sci., 244:437–440 (1989). The presence of, or the ability to induce the repertoire to produce, antibodies molecules capable of a catalyzing chemical reaction, i.e., acting like enzymes, had previously been postulated almost 20 years ago by W. P. Jencks in Catalysis in Chemistry and Enzymology, McGraw-Hill, N.Y. (1969).
It is believed that one reason the art failed to isolate catalytic antibodies from the immunological repertoire earlier, and its failure to isolate many to date even after their actual discovery, is the inability to screen a large portion of the repertoire for the desired activity. Another reason is believed to be the bias of currently available screening techniques, such as the hybridoma technique, towards the production high affinity antibodies inherently designed for participation in the process of neutralization, as opposed to catalysis.